The water-based ink has been extensively used as an ink for flexo printing, gravure printing or ink-jet printing.
In ink-jet printing methods, droplets of ink are directly projected onto a recording medium from very fine nozzles and allowed to adhere to the recording medium to form characters or images thereon. The ink-jet printing methods have become rapidly spread because of various advantages such as easiness of full coloration, low cost, capability of using a plain paper as the recording medium, non-contact with printed characters or images, etc.
In recent years, in the ink-jet printing methods, in order to impart good weathering resistance and good water resistance to printed matters, an ink for ink-jet printing which contains a pigment as a colorant and fine resin particles as a binder has been extensively used.
Also, in order to attain good adaptability to a nozzle head and further obtain printed matters having a high quality, a surfactant or an organic solvent has been used in the water-based ink for ink-jet printing.
For example, JP 2006-524269A (Patent Literature 1) discloses an ink-jet printing ink containing latex fine particles having a specific bulk density and a specific dielectric constant, and an effective amount of a surfactant adsorbed onto the surface of the respective latex fine particles. In JP 2006-524269A, it is also described that the ink is excellent in dispersion stability and printability.
JP 2009-155568A (Patent Literature 2) discloses a process for producing a water dispersion for ink-jet printing in which a mixture containing a colorant, polymer particles, a nonionic organic compound, a water-soluble surfactant and water is heat-treated at a temperature of not lower than 40° C. In JP 2009-155568A, it is also described that a water-based ink for ink-jet printing containing the water dispersion is excellent in ejection properties.
JP 2006-282759A (Patent Literature 3) discloses an ink composition including water-insoluble polymer particles that contain a pigment and are capable of dispersing the pigment in the ink composition, a surfactant and water, in which the surfactant contains acetylene glycol and an ethyleneoxide adduct of acetylene glycol at a specific weight ratio. In JP 2006-282759A, it is also described that the ink composition is excellent in color developability to a plain paper and glossiness to a glossy coated paper as well as election stability, etc.
JP 2011-195763A (Patent Literature 4) discloses an aqueous ink composition that includes at least a water-insoluble colorant, a glycol ether compound having an HLB value of 4.2 to 8.0, a 1,2-alkyl diol compound having 4 to 8 carbon atoms, resin particles, water and a silicone-based surfactant and/or an acetylene glycol-based surfactant. In JP 2011-195763A, it is also described that the ink composition is capable of forming images having excellent printing quality and rub fastness on a non-ink absorbing recording medium or a low-ink absorbing recording medium.
JP 2006-206688A (Patent Literature 5) discloses an ink composition for ink-jet printing including a pigment, a water-soluble organic solvent and a penetrant in which the ink composition includes a 1,2-alkanediol and an alkyl (having 3 or more carbon atoms) ether derivative of a glycol as the water-soluble organic solvent, as well as a specific polysiloxane-based surfactant and a specific acetylene glycol-based surfactant as the penetrant. In JP 2006-206688A, it is also described that with the ink composition, it is possible to suppress occurrence of rainbow-like image unevenness (iridescent mottling) on printed images.
JP 2006-282810A (Patent Literature 6) discloses an ink composition including a solid solution pigment constituted of two or more kinds of quinacridone-based compounds, a polyether-modified polydimethylsiloxane compound and water. In JP 2006-282810A, it is also described that the ink composition is capable of realizing formation of highly color-developed images and is excellent in ejection stability, etc.
JP 2015-124238A (Patent Literature 7) discloses an ink composition for ink-jet printing including three or more kinds of acetylene glycol-based surfactants, a coloring material and water in which a total content of the acetylene glycol-based surfactants is from 0.1 to 3% by mass on the basis of a whole mass of the ink composition. In JP 2015-124238A, it is also described that the ink composition is capable of forming printed images having excellent image quality and fusing properties at a high printing speed.
On the other hand, it has been required to form printed characters or images not only on a high-water absorbing recording medium such as the aforementioned conventional plain paper and so-called copy paper, but also on a low-water absorbing coated paper such as an offset-coated paper or a recording medium for commercial printing purposes which is surface-treated with a non-water absorbing synthetic resin film such as a polyvinyl chloride resin film, a polypropylene resin film and a polyester resin film.